function prototype declaration c

Question

Today I saw a function prototype of the form(few initial lines are added for completeness)

typedef unsigned char md5_byte_t; /* 8-bit byte */
typedef unsigned int md5_word_t; /* 32-bit word */
/* Define the state of the MD5 Algorithm. */
typedef struct md5_state_s {
    md5_word_t count[2];    /* message length in bits, lsw first */
    md5_word_t abcd[4];     /* digest buffer */
    md5_byte_t buf[64];     /* accumulate block */
} md5_state_t;

void md5_finish(md5_state_t *pms, md5_byte_t digest[16]);

This has been taken form md5 implementation of L. Peter Deutsch. From what I know writing 16 in the prototype does not make any sense. So why is it included here

Is it just a indication to programmer that whatever pointer or array you pass to the function it will only take into account the first 16 bytes of it. What does it actually signify here. here is the link to the implementation hosted at github

user195488 · Accepted Answer · 2012-07-16 17:52:25Z

7

In practice, it will decay to

void md5_finish(md5_state_t *pms, md5_byte_t *digest);

The 16 may be a hint to the size to use for the digest to the user, but the function technically will accept any size in the parameter, unless there is code in the function to check for a certain size.

answered Jul 16, 2012 at 17:52

user195488

Sign up to request clarification or add additional context in comments.

4 Comments

Aman Deep Gautam Over a year ago

For compiler only void md5_finish(md5_state_t *, md5_byte_t*); is sufficient, I know that but was just curious about why 16 has been written. Is it some kind of programming practice??

user195488 Over a year ago

@AmanDeepGautam: Must be some stylistic preference or like I said as a hint.

user195488 Over a year ago

@AmanDeepGautam: I looked at the code. You can pass a larger array into the function, and it will not matter. The for-loop in the function will only operate up to 16 bytes so the rest will just be ignored.

Aman Deep Gautam Over a year ago

Exactly. and this is why I feel that it is some kind of good programming practice to indicate that you just need to have 128 bits in your array(16 bytes) and the rest will not matter. There is also another thing that I found out that compiler will give you warnings if you pass array of size not equal to 16 an the warning goes away if you pass an array of size 16 to this function.

Collectives™ on Stack Overflow

function prototype declaration c

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related